Infra-red heat gun measures the surface temperature of the item that it is pointed to. If you check THE EXHAUST RUNNERS ONE AT A TIME & COMPARE THOSE TEMPS the coldest runner suggests that that cylinder is misfiring..

Has nothing to do with cracks in the exhaust..

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator